Typically, a circulatory support and cardioplegia administration system includes (among other things) a venous catheter for draining blood from the patient's venous system, a venous line for transferring blood drained with the venous catheter to a venous reservoir, a heat exchanger and an oxygenator connected via a transfer line to the outlet of the venous reservoir, and an arterial line connected to the outlet of the oxygenator to supply the oxygenated blood to a cannula, which returns the blood to the patient's heart. Such systems have included other components or subsystems as well. One such subsystem relates to blood recovery from the surgical site (e.g., the pericardial sack), and that system would include a number of blood suction devices (intracardiac suckers) that supply blood to a cardiotomy reservoir that collects, defoams and filters the recovered blood before supplying it to the venous reservoir of the main system.
Another subsystem is the cardioplegia administration system. Cardioplegia is a commonly used technique for protecting the heart during heart surgery. Typically, cooled cardioplegia solution (e.g., a potassium solution, cooled blood or a blood/potassium solution) is administered to the patient's heart in either the antegrade or retrograde direction through either the patient's aorta or coronary sinus, respectively. "Antegrade" refers to the direction of normal blood flow, and "retrograde" refers to the direction opposite of normal blood flow.
The cardioplegia solution stops the heart and reduces its temperature to minimize damage to the heart during surgery. Such cardioplegia solutions are typically introduced into the heart in an intermittent fashion. For example, a bolus of cooled cardioplegia solution may be delivered to the heart to initially arrest the heart, and then the subsequent doses of the cardioplegia may be administered approximately every 15-20 minutes.
Cardioplegia subsystems have included a heat exchanger connected to a source of cardioplegia solution and/or blood, a bubble trap to collect air emboli to prevent supplying such emboli to the patient, a temperature monitor for measuring and displaying the temperature of the cardioplegia solution downstream of the heat exchanger, a cardioplegia supply line connected to the outlet of the bubble trap/temperature monitor, and a catheter connected to the downstream end of the cardioplegia supply line for supplying the cardioplegia solution to the heart. Suitable catheters for retrograde administration of cardioplegia are disclosed in U.S. Pat. No. 4,927,412 (Menasche), and U.S. patent application Ser. No. 07/874,589, filed Apr. 27, 1992, on "Retrograde Coronary Sinus Catheter", by William G. O'Neill, Nelson L. Huldin, Sheila J. Hanson and John A. Covert, both of which are hereby incorporated by reference.
Heretofore, the cardioplegia heat exchanger has been separated from the patient by the substantial length (e.g., 8 feet (2.4 m)) of the cardioplegia supply line (plus the bubble trap/temperature monitor). A substantial volume of cardioplegia solution is held in the cardioplegia supply line, and this solution is being warmed by heat transfer through the cardioplegia supply line while it remains in that line. The result is that the initial cardioplegia solution being administered to the patient may be warmer than desired so that more cardioplegia solution must be administered to keep the temperature of the heart down. In addition to the delay in cooling the heart, the additional cardioplegia solution required due to this warming results in administering additional quantities of a drug (potassium solution) to the patient than would otherwise be required.
One approach to this problem has been to recirculate the cardioplegia solution in the cardioplegia delivery line back to the heat exchanger to re-cool it. That approach involves opening a clamp on a recirculation line when the delivery line is closed adjacent the catheter.